This invention relates to metal oxide and/or organofunctionalized metal oxide coated metal oxide particles, where the two metals are not the same. Such materials are obtained by reaction of the pre-formed particles with a monomeric precursor to the coating, and characterized by extremely high levels of uniformity in coating thickness over both the surface of individual particles and the particle population.
In many applications using titania particles as a white pigment, the lifetime of the pigmented material, paints or plastics for example, is reduced by chemical processes initiated by photo-excitation of the pigment particles. As a result, technologies to improve the durability of pigmented objects have been developed which suppress the photocatalytic activity of titania pigments. The most successful approach to this problem has been coating the particles with silica or silica/alumina layers. Pigments with silica coatings at 1.5-2.0 weight % are characterized as "durable" pigments, and at 5-6 weight % are described as "high durability" pigments.
These efforts to reduce photocatalytic activity of titania pigments are not without disadvantages. First, pigment gloss degrades rapidly with added silica. High gloss and durability are therefore difficult to attain simultaneously in products based on this approach. Second, titania particles with pure silica surfaces do not disperse well in many of the vehicles in which pigments are used. This requires additional surface treatments, typically involving deposition of partially crystalline alumina layers. Therefore, other methods for suppressing the inherent photoactivity of pigment particles are of interest, either to minimize the severity of the tradeoffs in the properties of the finished pigment, or to confer cost or flexibility advantages in new manufacturing production facilities.